list :(部分 View )
MainActivity，程序立即终止并在日志中发出消息。
它应该已经开始显示按钮来选择继续执行的选项。
经过几天的研究这个论坛，我发现一些帖子建议将 BackupDb 放置在应用程序的 list 中。
完成此操作后，我最终在日志中看到了该消息。
在耗尽了我的研究空间后，我想知道可能存在什么问题以及如何解决它。
list :(部分 View )
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.peter.databasetest"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="16"
android:targetSdkVersion="19" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<supports-screens
android:xlargeScreens="true"
android:largeScreens="true"
android:normalScreens="true"
android:smallScreens="false"
/>
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme"
**android:name="com.peter.databasetest.BackupDB">**
<activity
android:name="com.peter.databasetest.MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".CheckDatabase"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.CHECKDATABASE" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name=".CheckSDcard"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.CHECKSDCARD" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name="com.peter.databasetest.Insert"
android:label="@string/app_name" >
<intent-filter>
<action android:name="com.peter.databasetest.INSERT" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
</application>
</manifest>
MainActivity:调用 checkSDcard 和 CheckDatabase。检查是否存在 SDCard 以及 main 中的数据库是否存在。
public class MainActivity extends Activity implements OnClickListener {
DBAdapter db;
Button insertButton; //ADD A NEW RECORD
Button listAllButton; //LIST ALL
Button cancelButton; //CANCEL PGM
Button backupDbButton; //REQUEST BACKUP DB TO SDCARD
Button restoreButton; //RESTORE DB FROM SDCARD TO MAIN
Button memsizeButton; //SHOW MEMORY SIZES ON DEVICE
int retcode;
int chk;
String message;
public Context context;
public static final String NO_DB ="Database does not exist. Backup is not possible";
public static final String DB_PB ="ERROR- Check log";
public static final String UNWR_SDCARD ="Your SDCard must be set to writable. Check the card lock";
public static final String NO_SDCARD ="No SDcard detected. No backup is possible";
public static final String BKP_OK = "Backup was SUCCESSFUL.";
public static final String BKP_NOK = "Backup FAILED. ";
static final int SD_CHECK = 1;
static final int DB_CHECK = 2;
static final int BK_CHECK = 3;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
insertButton = (Button) findViewById(R.id.insertButton);
listAllButton = (Button) findViewById(R.id.listAllButton);
cancelButton = (Button) findViewById(R.id.cancelButton);
backupDbButton = (Button) findViewById(R.id.backupDbButton);
restoreButton = (Button) findViewById(R.id.restoreButton);
memsizeButton = (Button) findViewById(R.id. memsizeButton);
insertButton.setOnClickListener(this); //insert record into DB
listAllButton.setOnClickListener(this); //list ALL records from DB
cancelButton.setOnClickListener(this); //cancel the program
backupDbButton.setOnClickListener(this); //request backup to sdcard
restoreButton.setOnClickListener(this); //request restore from sdcard
memsizeButton.setOnClickListener(this); //Get Meory sizes
public void onClick(View v ) {
if (v == insertButton) {
startActivity(new Intent(getApplicationContext(), Insert.class));
}else if (v == listAllButton){
startActivity (new Intent(MainActivity.this, ListDr.class));
}else if (v == backupDbButton){
**Intent checksd = new Intent(this,CheckSDcard.class);**
**startActivityForResult(checksd, SD_CHECK);**
}else if (v == restoreButton) {
startActivity (new Intent(MainActivity.this,RestoreDB.class));
}else if (v == memsizeButton) {
startActivity (new Intent(MainActivity.this,GetMemorySizes.class));
}else if (v == cancelButton){
finish();
}
}
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if (requestCode == SD_CHECK && resultCode == RESULT_OK) {
Intent checkdb = new Intent(MainActivity.this,CheckDatabase.class);
startActivityForResult(checkdb, DB_CHECK);
}else if (requestCode == DB_CHECK && resultCode == RESULT_OK){
**Intent backup = new Intent(MainActivity.this,BackupDB.class);**
**startActivityForResult(backup, BK_CHECK);**
}else if (requestCode == BK_CHECK && resultCode == RESULT_OK){
message = BKP_OK;
SendMessageDialog(message);
finish();
}
if(resultCode == RESULT_CANCELED && resultCode == -1){
message = NO_DB;
SendMessageDialog(message);
finish();
}else if(resultCode == RESULT_CANCELED && resultCode == -2) {
message = DB_PB;
SendMessageDialog(message);
finish();
}
}
BackupDb:将数据库复制到SDCARD。
package com.peter.databasetest;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.channels.FileChannel;
import android.app.Activity;
import android.app.AlertDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import com.peter.databasetest.DBAdapter;
public class BackupDB extends AsyncTask<Void, Void, Integer> {
DBAdapter db;
intrc= -10;
intretcode;
intchk;
Stringmessage;
String mypackage;
public Context context;
public static String FOLDER_NAME = "DBfolder";
public static final String DATABASE_NAME = "UserDB.db";
public static final String DATABASE_BACKUP= "UserDB.db";
public static final String BKP_OK = "Backup was SUCCESSFUL.";
public static final String BKP_NOK = "Backup FAILED. ";
@Override
protected void onPreExecute() {
// GET PACKAGE NAME
mypackage = context.getApplicationContext().getPackageName() ;
}
// START BACKUP TO SDCARD
@Override
protected Integer doInBackground(Void... params) {
// DOING BACKUP
Log.i("00000" , "STARTING BACKUP...BACKUP ");
File sd = Environment.getExternalStorageDirectory();
File data = Environment.getDataDirectory();
CREATE A FOLDER /mnt/sdcard<packagename>FOLDER_NAME if it does not exist
File folder = new File(Environment.getExternalStorageDirectory()
+ "/"
+ mypackage
+ "/"
+ FOLDER_NAME);
if(!folder.exists()) {
if (folder.mkdirs()) ;
}
// GET THE PATH OF THE BACKUP ON THE SDCARD
FilefileBackupDir = new File(Environment.getExternalStorageDirectory()
+ "/"
+mypackage
+ "/"
+ FOLDER_NAME
+"/"
+ DATABASE_BACKUP) ;
// IF WE HAVE A BACKUP ON SDCARD, DELETE IT TO MAKE ROOM FOR THE NEW BACKUP
if (fileBackupDir.exists()) {
fileBackupDir.delete();
}else {
* DO NOTHING */
}
// GET CURRENT DB PATH FOR THE COPY
String currentDBPath = "/data/" + mypackage + "/databases/"+ DATABASE_NAME;
// GET CURRENT DB PATH FOR THE BACKUP
String backupDBPath = "/" + mypackage + "/" +FOLDER_NAME + "/" + DATABASE_BACKUP;
FilecurrDB = new File(data, currentDBPath) ;
FilebkpDB = new File(sd, backupDBPath);
FileChannel from = null;
try {
from = new FileInputStream(currDB).getChannel();
} catch (FileNotFoundException e) {
e.printStackTrace();
}
FileChannel to = null;
try {
to = new FileOutputStream(bkpDB).getChannel();
} catch (FileNotFoundException e) {
e.printStackTrace();
}
try {
to.transferFrom(from, 0, from.size());
} catch (IOException e) {
e.printStackTrace();
}
try {
from.close();
} catch (IOException e) {
e.printStackTrace();
}
try {
to.close();
} catch (IOException e) {
e.printStackTrace();
}
retcode = 0;
returnretcode;
// end DoInBackgroung
protectedvoid onPostExecute(Integer retcode, String message) {
if(retcode == 0) {
message = BKP_OK;
SendMessageDialog(message);
}else {
message = BKP_NOK;
SendMessageDialog(message);
}
}
public void SendMessageDialog(String message) {
if (message == BKP_OK ) {
AlertDialog.Builder builder = new AlertDialog.Builder(context);
builder.setTitle("My Database")
.setMessage(message) // Title of the dialog
.setCancelable(true) // Does allow the use of Back Button on the hardware
.setIcon(R.drawable.ecg)// da picture
.setPositiveButton("OK", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
dialog.dismiss();
dialog.cancel();
}
});
final AlertDialog alert = builder.create();
alert.show();
}else {
AlertDialog.Builder builder = new AlertDialog.Builder(context);
builder.setTitle("My Database")
.setMessage(message) // Title of the dialog
.setCancelable(true) // Does allow the use of Back Button on the hardware
.setIcon(R.drawable.bad)// da picture
.setPositiveButton("OK", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
dialog.dismiss();
dialog.cancel();
}
});
final AlertDialog alert = builder.create();
alert.show();
}
}
}
日志猫:
02-12 07:36:06.015: E/AndroidRuntime(987): FATAL EXCEPTION: main
02-12 07:36:06.015: E/AndroidRuntime(987): java.lang.RuntimeException: Unable to instantiate application com.peter.databasetest.BackupDB:
: com.peter.databasetest.BackupDB cannot be cast to android.app.Application
02-12 07:36:06.015: E/AndroidRuntime(987): at android.app.LoadedApk.makeApplication(LoadedApk.java:501)
02-12 07:36:06.015: E/AndroidRuntime(987): at android.app.ActivityThread.handleBindApplication(ActivityThread.java:4124)
02-12 07:36:06.015: E/AndroidRuntime(987): at android.app.ActivityThread.access$1300(ActivityThread.java:130)
02-12 07:36:06.015: E/AndroidRuntime(987): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1255)
02-12 07:36:06.015: E/AndroidRuntime(987): at android.os.Handler.dispatchMessage(Handler.java:99)
02-12 07:36:06.015: E/AndroidRuntime(987): at android.os.Looper.loop(Looper.java:137)
02-12 07:36:06.015: E/AndroidRuntime(987): at android.app.ActivityThread.main(ActivityThread.java:4745)
02-12 07:36:06.015: E/AndroidRuntime(987): at java.lang.reflect.Method.invokeNative(Native Method)
02-12 07:36:06.015: E/AndroidRuntime(987): at java.lang.reflect.Method.invoke(Method.java:511)
02-12 07:36:06.015: E/AndroidRuntime(987): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
02-12 07:36:06.015: E/AndroidRuntime(987): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
02-12 07:36:06.015: E/AndroidRuntime(987): at dalvik.system.NativeStart.main(Native Method)
02-12 07:36:06.015: E/AndroidRuntime(987): Caused by: java.lang.ClassCastException: com.peter.databasetest.BackupDB cannot be cast to android.app.Application
02-12 07:36:06.015: E/AndroidRuntime(987): at android.app.Instrumentation.newApplication(Instrumentation.java:982)
02-12 07:36:06.015: E/AndroidRuntime(987): at android.app.Instrumentation.newApplication(Instrumentation.java:967)
02-12 07:36:06.015: E/AndroidRuntime(987): at android.app.LoadedApk.makeApplication(LoadedApk.java:496)
02-12 07:36:06.015: E/AndroidRuntime(987): ... 11 more
评论: 我从应用程序中删除了 BackupDb 并将其恢复为 Activity 。
<activity
android:name=".BackupDB"
android:label="@string/app_name" >
<intent-filter>
<action android:name="com.peter.databasetest.BACKUPDB" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
程序现在按预期显示按钮，但在尝试备份时，我仍然收到与之前日志中相同的消息。 (第二十二条军规？)
最新日志:
02-12 13:00:16.569: W/dalvikvm(30656): threadid=1: thread exiting with uncaught exception (group=0x40a13300)
02-12 13:00:16.650: E/AndroidRuntime(30656): FATAL EXCEPTION: main
02-12 13:00:16.650: E/AndroidRuntime(30656): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.peter.databasetest/com.peter.databasetest.BackupDB}: java.lang.ClassCastException: com.peter.databasetest.BackupDB cannot be cast to android.app.Activity
02-12 13:00:16.650: E/AndroidRuntime(30656): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1983)
02-12 13:00:16.650: E/AndroidRuntime(30656): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
02-12 13:00:16.650: E/AndroidRuntime(30656): at android.app.ActivityThread.access$600(ActivityThread.java:130)
02-12 13:00:16.650: E/AndroidRuntime(30656): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
02-12 13:00:16.650: E/AndroidRuntime(30656): at android.os.Handler.dispatchMessage(Handler.java:99)
02-12 13:00:16.650: E/AndroidRuntime(30656): at android.os.Looper.loop(Looper.java:137)
02-12 13:00:16.650: E/AndroidRuntime(30656): at android.app.ActivityThread.main(ActivityThread.java:4745)
02-12 13:00:16.650: E/AndroidRuntime(30656): at java.lang.reflect.Method.invokeNative(Native Method)
02-12 13:00:16.650: E/AndroidRuntime(30656): at java.lang.reflect.Method.invoke(Method.java:511)
02-12 13:00:16.650: E/AndroidRuntime(30656): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
02-12 13:00:16.650: E/AndroidRuntime(30656): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
02-12 13:00:16.650: E/AndroidRuntime(30656): at dalvik.system.NativeStart.main(Native Method)
02-12 13:00:16.650: E/AndroidRuntime(30656): Caused by: java.lang.ClassCastException: com.peter.databasetest.BackupDB cannot be cast to android.app.Activity
02-12 13:00:16.650: E/AndroidRuntime(30656): at android.app.Instrumentation.newActivity(Instrumentation.java:1053)
02-12 13:00:16.650: E/AndroidRuntime(30656): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1974)
02-12 13:00:16.650: E/AndroidRuntime(30656): ... 11 more
>Question:
>Is there any known limitation calling an AsyncTask by way of startActivityForResult?
>Could this be a factor?
最佳答案
问题出在 Manifest 文件中，您将 application:name 设置为 BackupDB 类，并且该类只是一个 AsyncTask 而不是 Application。
从“android:name”的解释可以看出:
An optional name of a class implementing the overall
android.app.Application for this package. [string]
关于java - 无法实例化应用程序 java.lang.RuntimeException :. ..BackupDB 无法转换为 android.app.Application，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/21736298/